Tubal ligation and incidence of 26 site-specific cancers in the Million Women Study

BACKGROUND: Tubal ligation is known to be associated with a reduction in ovarian cancer risk. Associations with breast, endometrial and cervical cancers have been suggested. We investigated associations for 26 site-specific cancers in a large UK cohort. METHODS: Study participants completed a questionnaire on reproductive and lifestyle factors in 1996–2001, and were followed for cancer and death via national registries. Using Cox regression models, we estimated adjusted relative risks (RRs) for 26 site-specific cancers among women with vs without tubal ligation. RESULTS: In 1 278 783 women without previous cancer, 167 430 incident cancers accrued during 13.8 years' follow-up. Significantly reduced risks were found in women with tubal ligation for cancers of the ovary (RR=0.80, 95% CI: 0.76–0.85; P<0.001; n=8035), peritoneum (RR=0.81, 0.66–0.98; P=0.03; n=730), and fallopian tube (RR=0.60, 0.37–0.96; P=0.04; n=168). No significant associations were found for endometrial, breast, or cervical cancers. CONCLUSIONS: The reduced risks of ovarian, peritoneal and fallopian tube cancers are consistent with hypotheses of a common origin for many tumours at these sites, and with the suggestion that tubal ligation blocks cells, carcinogens or other agents from reaching the ovary, fallopian tubes and peritoneal cavity.